1. Field of the Invention
This invention relates to slit valves. More particularly, this invention relates to slit valves which are useful as automatic valves in the proximal portions of trocar assemblies.
2. State of the Art
Endoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, endoscopic surgery involves one or more incisions made by trocars where trocar tubes are left in place so that endoscopic surgical instruments may be inserted through the tubes. Various surgical viewing telescopes, cameras, lenses, or other viewing instrumentation are inserted through one or more trocar tubes, while a cutter, dissector, or other surgical instrument is inserted through another trocar tube for the purpose of manipulating and/or cutting the internal organ or tissue. Sometimes it is desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organs or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon via the viewing instrumentation in place.
By 1996, it is expected that more than two million additional endosurgeries will be performed per year that, in 1990, were done via open surgery (MedPRO Month, I:12, p.178). The advantages of endoscopic surgery are clear in that it is less invasive, less traumatic and recovery is typically quicker. As a result, many new instruments and devices for use in endosurgery are introduced every year.
Several advances have been made in the art of trocars and trocar tubes. In general, a trocar (stylet) is inserted into a trocar tube (cannula) so that the distal end of the solid trocar extends beyond the distal end of the hollow trocar tube. The trocar and trocar tube are inserted together into the patient's body and the trocar is then removed from the trocar tube leaving the trocar tube in the patient's body to act as a pathway for the subsequent insertion of endoscopic tools. Trocar tubes are also used for insufflation and desufflation of certain fluids such as the insufflation of CO.sub.2 under pressure during various endoscopic procedures. In these applications, trocars must be fitted with some type of sealing mechanism to prevent the leakage of gasses. U.S. Pat. No. 3,994,287 to Turp et al. discloses a disposable plastic trocar tube having a flange portion containing a sealing valve assembly. The valve assembly consists of an elastic ring with an axial opening of reduced diameter. The elastic ring acts as a sealing gasket between the endoscopic tool and the proximal opening of the trocar.
While the introduction of sealing valve means in trocars has definite advantages, disassembly of the valves for cleaning, and the subsequent reassembly and sterilization of these valves is often difficult and time consuming. This is particularly so with more sophisticated valves such as the ball valve disclosed in U.S. Pat. No. 4,379,458 to Bauer et al. As a result of the difficulties in cleaning the valves of the reusable trocars, a large disposable trocar market has emerged. The use of disposable trocars, however, is costly both in actual per operation equipment costs, as well as in the disposal of the medical waste.
Other improvements in trocar assemblies include various safety systems which sometimes interact with sealing valve mechanisms to prevent accidental punctures by the sharp distal end of the trocar. U.S. Pat. No. 4,654,030 to Moll et al. discloses a trocar having a coaxial spring loaded safety shield which extends over the distal sharp point of the trocar. A trocar tube having an elastomeric gasket and a flapper valve interacts with the safety shield so that the sharp point of the trocar can only be exposed when the flapper valve is opened. Similar arrangements are disclosed in U.S. Pat. No. 4,931,042 to Holmes et al. and U.S. Pat. No. 5,032,206 to Lander.
Other innovations in trocar tubes include the addition of helical threads on the surface of the trocar tube, as shown in U.S. Pat. No. 5,009,643 to Reich et al., in order to better hold the trocar tube in place in the patient.
Perhaps the most commonly used trocar assembly today is the safety trocar with flapper valve assembly similar to those described by Moll et al., Holmes et al., and Lander. Some of the improvements to these types of trocars include an improved valve seat and plug for the flapper valve to assure a gas-tight seal when the flapper valve is closed as is described in U.S. Pat. No 5,053,016 to Lander. It is, however, a continuing disadvantage of trocar tubes having sealing valves that they are either difficult to disassemble, sterilize, and reassemble, or alternatively that they are intended for disposal after a single use. These disposable trocar tubes are relatively expensive and, as mentioned above, endoscopic surgical procedures often require several trocar tubes to be in use simultaneously.